Disposable absorbent articles are broadly available and consumers are used to a high performance for the collection and retention of menses (in the case of sanitary napkins or panty liners) or for the collection and retention of urine and fecal material (in the case of e.g. disposable diapers). However, consumers do not only expect a superior absorbency behaviour, but place more and more emphasis on the wearing comfort of such articles, and namely on the dryness of those articles. Typically, such articles comprise multiple absorbent layers, at least one layer being primarily designed to store liquid (storage layer), and at least one other layer primarily designed to acquire and/or distribute liquid (acquisition layer). The storage layer may include super-absorbent material that is admixed with the traditionally used pulp fiber material. Such super-absorbent materials may be adapted to absorb many times (e.g. 10, 20, or 30 times) their own weight, and therefore be desirable when designing an article of improved fluid handling properties. Recent absorbent articles may employ higher concentrations of super-absorbent material than absorbent articles of the past, for example concentrations of superabsorbent material in excess of 50% of the total weight of the storage member. These products may achieve a relatively high absorbing capacity with a relatively thin storage member, thereby potentially reducing the overall thickness of the absorbent article product. While super-absorbent materials may be capable of storing substantial amounts of liquid, they may not able to distribute the liquid from the point of impact to more remote liquid storage areas of the absorbent article as fast as the liquid is discharged to the article. For this reason acquisition layers may sometimes be included in an absorbent article. Acquisition layers are typically configured to provide for the interim acquisition of liquid and for the distribution of liquid to various regions of the storage layer. After the initial acquisition of liquid by the acquisition layer, the liquid may subsequently be absorbed by and finally stored in the storage layer. Thus, the acquisition layer may provide a desirable way to maximize the absorbent capacity of the storage layer. An example of an acquisition layer is disclosed in PCT Publication No. WO 95/34710.
Besides initial acquisition and distribution of liquids, another factor that may be considered when evaluating the performance of disposable absorbent articles is the absorbent capacity of the super-absorbent material in the storage layer. Super-absorbent materials may be provided in the form of super-absorbent polymers (SAPs), which are lightly crosslinked hydrophilic polymers that can absorb up to about one hundred times their own weight, or more, of distilled water. One commonly used SAP for absorbing electrolyte-containing liquids such as urine, is partially crosslinked, neutralized polyacrylic acid including for example 50% to 75% or 70% to 100% neutralized carboxyl groups. One desirable quality of an SAP in a hygienic article, such as a diaper, may include the ability to retain the absorbed fluid under a confining pressure. In at least some instances, the swelling and absorbent properties of SAPs may be attributed to (a) electrostatic repulsion between the charges along the polymer chains, and (b) osmotic pressure of the counter ions. However, it is commonly known in the art that these absorption properties are reduced in solutions containing electrolytes, such as saline, urine or blood. Thus, SAPs may function less effectively in the presence of such physiologic fluids. This decrease in absorption capacity is often referred to as “salt poisoning”.
There have been attempts to counteract the salt poisoning effect by removing salts. For example, see US 2003/0144379 to Mitchell, et al.; PCT Publication No. WO 99/33843 to Garoff, et al.; PCT Publication No. WO98/37149 to Goldman; WO 92/20735 to Tanaka, et al.; EP 0 210 756 A1 to Wong; JP 57-35938 A2; JP 11-89878 A2; and JP 01-164436 A2.
Besides salt poisoning, the absorption capacity of SAPs may also be reduced by reducing the degree of neutralization, e.g by acidifying liquids. U.S. Pat. No. 4,657,537 describes a disposable absorbent articles having an ion-exchanging topsheet. This topsheet exchanges only cations against protons. It does not remove anions and it acidifies the liquid by lowering the pH.
It may be desirable to provide material for the acquisition of electrolyte containing liquids with good acquisition, distribution and/or absorption properties. It may also be desirable to provide an improved acquisition material based on acid crosslinked cellulosic fibers which reduce the electrolyte concentration of a liquid without acidifying the liquid.